The cascaded H-bridge APF is one of the best solutions for suppressing harmonics and compensating reactive current in the medium voltage field, but the balance of DC side voltage has become a difficult problem for its application. Therefore, the mathematical model of cascaded APF in medium voltage is established and its fluctuating process is analyzed in detail, and an improved hierarchical control method based on DC side voltage is proposed. The upper voltage-stabilizing control combines the improved ip-iqalgorithm, and adjusts the active current command in real time according to adaptive PI parameters, keeping the balance of the total voltages each phase; the lower voltage-sharing control is said that a modulation signal component based on the unitized current is compensated to the main modulation wave, which can achieve voltage balancing each unit. At the same time, the device not only improves the detection accuracy and response speed of harmonic current, but also achieves the purpose of APF for tracking current and compensating reactive power. Finally, validity of the method is verified by simulation and experiment for the APF to apply in a medium voltage level.
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